Hiro, My Little Test Subject
by MaturePopcorn
Summary: When Tadashi decides to make Baymax, he needs a LOT of information for him about people and the human body. But Baymax can only learn so much from books and the internet; some of it has to come from real-life experiences. And who better to help Tadashi than his own brother…
1. Chapter 1

**"Hiro, My Little Test Subject"**

_By MaturePopcorn_

**Description: **When Tadashi decides to make Baymax, he needs a LOT of information for him about people and the human body. But Baymax can only learn _so much_ from books and the internet; some of it has to come from real-life experiences. And who better to help Tadashi than his own brother…

**WARNING: **Is a warning really necessary? You clicked on a RATED M+++ FIC. TRUST ME; UNLESS YOU'RE NINE, YOU KNOW WHAT YOU'RE GETTING INTO. So no warning is needed, right? No? Good.

**_Author's note:_** STOPSTOPSTOP DROP EVERYYYTHIIING…! BIG HERO 6 IS OUT, NOTHING ELSE MATTERS. I _WAS _in the middle of writing a Naruto _x_ Gaara fic. (Which I'll finish and post within a week; see my account later…), when I went to go see Big Hero 6 with my friends. I had high expectations…

…And I was not disappointed.

All other fanfictions are being placed on hold until this one-shot is completed and posted. Sorry for the (not really an) inconvenience.

Much love,

~Kisa Alvarez

**Chapter 1**

Tadashi leaned back in his chair and sighed. He had been searching for hours, but couldn't find what he was looking for… Porn. But it wasn't for him. He NEEDED Baymax to learn everything about the human body, including sex, and simply giving Baymax an internet Sex Ed. class wasn't enough; he had to show Baymax videos of it actually happening to get the fullest amount of information. The easiest place to get videos was a porn website. However, Aunt Cass strictly monitored the internet (mainly for Hiro) and the college blocked porn. The only thing he could think of was live sex, which he could film and upload to a disk for Baymax. But Tadashi seriously doubted that anyone at the college would actually let him use their bodies for science, as much as they all loved it and respected Tadashi. He tried to think of another way, to "look for another angle", but all he came up with was frustration and annoyance.

"Tadashi! Hiro! Dinner's ready! I made pizzaaas!"

Hiro bolted from his bed over on the other side of the screen and ran downstairs, grinning and singing, "Yeaaah, pizza…!" He slipped and fell on the bottom stair, quickly standing back up. "I'M OKAY!" He ran over to his chair and sat there, wide eyed, waiting impatiently. Tadashi slowly followed him, sitting down next to him. He looked at Hiro and rolled his eyes, smiling. _"Crazy kid…"_ He looked around the table, but there were no plates. He looked up confused. "Umm… Aunt Cass?"

Aunt Cass smiled at Tadashi, "I know; the dishwasher just finished drying the dishes. Hiro, can you go get some plates while I take the pizza out of the oven?"

Hiro got out of his place. "Sure, Aunt Cass." He walked over and opened the dishwasher. Tadashi happened to be watching him, and when Hiro bent over, Tadashi's eyes wandered to his brother's butt. He blushed and looked away, but he couldn't stop himself from looking again. _"H-has Hiro always been THAT cute?" _Tadashi blushed harder and looked down, mortified at the thoughts circulating in his mind. Hiro set the table and sat down, looking at Tadashi quizzically. "Hey bro, you okay?"

Tadashi looked at his confused face, and something in his head instantly clicked. He smiled and tussled Hiro's hair. "Yeah, just thinking about something. When dinner's done, I wanna show you something I've been working on, 'K?"

Hiro grinned. "Sure!"

Aunt Cass sat down and put the pizza on the table. "You boys okay? How was school today, Tadashi?"

Tadashi served himself some pizza. "Good. I'm almost done with my 'project'; I just need one more thing."  
>Aunt Cass smiled. "That's great! If you need, I can go get it. I'm going out to the store, but I have to go all the way to San Rasaka; United Markets is the only place I can get <em>all<em> my stuff." She looked at them warily. "You won't burn the house down with one of your experiments, right? You won't get arrested?"

Both boys rolled their eyes. "No, Aunt Cass…"

Aunt Cass smiled. "Good! So, what was it you needed?"

Tadashi looked up with a mouth full of pizza. "Yu knt git it nt ha stohre."

Aunt Cass's left eye twitched. "Tadashi, that's disgusting."

Tadashi swallowed. "I said 'you can't get it at the store.'" He glanced at Hiro. "It's not something you can really buy, it's information."

Aunt Cass took a sip of wine. "Well, I should be back in two hours or so."

Hiro looked at Aunt Cass judgingly. "Should you be drinking that if you're driving?"

Aunt Cass laughed, "I'm only having this one glass, Hiro; I'll be fine."

Hiro shrugged and kept eating.

Tadashi smiled. _"Two hours, huh? That's all the time I need…" _He thought, glancing over at Hiro every now and then.

When they were done with dinner, the two teens headed upstairs while their Aunt Cass left for the store.

"Be safe, and don't go outside!" she yelled upstairs. "It's dark, and KRON4 said it's going to rain tonight!"

"We won't Aunt Cass! We'll be good!"

Aunt Cass smiled and locked up the door behind her, leaving Tadashi and Hiro alone in the house together.

Hiro walked over to Tadashi's side of the room. "So, big bro, what were you gonna show me?"

Tadashi grinned really big. "Well, you know that 'thing' I'm working on?"

Hiro sighed. "You mean the one you talk about non-stop but never show anyone? Yeeesss… What about it…?"

Tadashi looked around at the messy room until his eyes settled on a camera. "Well, it's a robot, like the ones you make. Only thing is, I'm missing some key information, so I was hoping you could help me." He walked over to the camera he had got for his twelfth birthday and set it on a tripod. He looked at Hiro. "'K?"

Hiro nodded. "I guess. What kind of information?"

Tadashi shot Hiro a half smile and turned the camera on. Then, after pressing play, he took his shirt off. "Come here, lil' bro."

Hiro warily walked across the room to Tadashi. "What are you doi-HEY!" Tadashi grabbed Hiro's waist and pulled his pants down around his ankles. Hiro squirmed away and fell down. "W-what the hell are you doing?!"

Tadashi grinned. "Come on, I need this to finish my robot."

Hiro looked at Tadashi with a full look of WTF. "What… You…? No! I-I'm your BROTHER!"

Tadashi looked slightly annoyed. "You don't even know what I was gonna do."

Hiro whimpered, causing Tadashi's dick to get harder. He unbuttoned and unzipped his pants, pulling them down a couple inches so his bulge stuck out. "But… You probably guessed right anyway…"

Hiro blushed insanely red and backed up a few feet, into his dresser. The honest truth was that he had these fantasies all the time; he usually jacked off at night to the thought of Tadashi "doing things" to him. But now that Tadashi really wanted to do them, Hiro was confused and alarmed. _"I mean… I want it **sooo **bad, but Tadashi is my BROTHER!" _Hiro glanced up at his big brother. _"And… I'm 14, he's 19… It would be illegal even if he wasn't my brother! He could get in serious trouble."_

Tadashi sighed and looked at Hiro. "Hey, lil' bro. Your bulge is sticking out."

Hiro looked down and decided, right then, that he _definitely _needed this. He squirmed a little in embarrassed anguish and emotional agony, rubbing his tip against the front of his underwear, sending waves of pleasure down his body. "I… I guess we could maybe do a LITTLE before Aunt Cass gets home…?"

Tadashi smiled wide. He walked over to his little brother and got on his knees, lifting Hiro's shirt up and using his tongue to feel every inch of Hiro's chest. "T-Tadashi… Nnghh…!" Hiro blushed harder than he thought physically possible and looked down at Tadashi. "T-this is so… Wrong! I-I don't think we…"

Tadashi put his first two fingers on Hiro's lips and hushed him, smiling. "Don't think at all. Just let your instinct take over." He then leaned in close to his little brother's mouth and gently brushed their lips together before pulling away to softly bite Hiro's neck, moving down onto his collarbone. He kissed him softly, working his way further down to his bellybutton, before rubbing his head against Hiro's chest quietly. "You know, I really love you, Hiro."

Hiro breathed in and moaned softly as Tadashi pulled the band of his underwear down, sticking his hand down where his boyhood stuck out, hard as a rock, pushing against Tadashi's prominent boner. He looked at Tadashi with eyes of submission and breathed, "I love you too, Tadashi."

Tadashi smiled with genuine love and pure happiness. He reached down and grabbed Hiro's shaft and balls with one hand, using the other to pull down his little brother's underwear lower so his boyhood was fully exposed. He brought his face back up to Hiro's and, more forcefully this time, pressed his lips against Hiro's and forced his lips apart with his tongue, ramming it into Hiro's mouth all the way back to his throat. Hiro squirmed and moaned loudly, pushing back and digging his nails into Tadashi's back as he began to pump Hiro's dick, sending more waves of pleasure down Hiro's body. Tadashi grinned and looked at Hiro with eyes of pure lust before taking his hand away from his brother's crotch. Hiro whined, "N-no…! Don't stop…"

Tadashi breathed heavily, "I'm not, lil' bro; don't worry, I have something even better…" He moved down until his face was directly over Hiro's crotch, burying his face in it. He wrapped his lips around one hairless ball, then the other, and wrapped his hand around Hiro's cute little body so he could hold his ass in his hands, squeezing it gently. Hiro moaned softly and grabbed Tadashi's hair with his hands. Tadashi moved his fingers over and stuck two of them a cm. up Hiro's tight little hole. Hiro gasped and dug his nails back into the back of Tadashi's head, making him wince in pain.

"S-sorry…! But… You…"

Tadashi slowly shook his head, not wanting to dare lose Hiro's taste. Instead, he slowly forced his fingers up further into the hole until they were in up to his knuckle. Hiro was moaning every other breath by now and felt like he was on ecstasy, wanting nothing more than this feeling to last forever. He started slowly grinding on his big brother's hand to make it feel even better, forcing the fingers in and out just a little. He looked into Tadashi's eyes expectantly, and Tadashi answered his silent pleas with his mouth, taking the balls out and putting Hiro's tip into his mouth. Hiro was only about 11 cm. but it was still enough to fill Tadashi's mouth when he put it in deeper. He even went as far as fitting the whole thing in his mouth AND putting Hiro's balls in his mouth, filling it to the brim with his little brother's husky tasting, hairless crotch. Hiro let out a loud moan of pleasure and softly screamed, "Tadashiii…!" He pulled on Tadashi's hair, forcing his big brother to suck with increasing force and determination.

Within five minutes, the younger teen couldn't take it anymore. He came, with a huge moan, directly down Tadashi's throat; the smooth, creamy, hot liquid streaking down and spilling out his mouth, leaving white puddles on Hiro's inner thighs and the bed sheets. Hiro put the back of his hand over his mouth to stop from screaming too loud, moaning Tadashi's name so loud they were convinced the neighbors could hear. Tadashi slowly took Hiro's boyhood out of his mouth, leaving a thin line of cum and precum from his mouth to Hiro's tip.

Tadashi's erect boner felt like it was going to burst from non-use, and he looked at Hiro's quivering, naked body lying on the bed. Hiro now wore nothing but black half-knee socks and his underwear was down around his ankles, which turned Tadashi on even more, if that were even possible. He grabbed Hiro's waist and butt and slowly flipped him over onto his stomach, to which he made soft noises the whole time. He forced Hiro's cheeks apart and looked at his little brother's tight little hole, which was barely stretched at all from his fingers. He grabbed Hiro's wrists and forced him onto his hands and knees; he then climbed over Hiro and mounted himself right above his hole with his 21 cm. cock. Hiro whimpered softly. "T-Tadashi… Will this hurt? You're so big…"

Tadashi blushed like crazy. "I-it might a little at first, like my hand did… But it'll feel really good soon, I promise…" Using nothing but sweat and precum as lube, Tadashi slowly forced his cock into his little brothers hole. Hiro moaned, softly at first, then VERY loud, and when Tadashi stopped halfway in, Hiro thrust backwards to ram the rest of it all the way in.

He stopped, and he felt a severe pain in his ass. He looked back to see that a small amount of blood was dripping onto the bed from where Tadashi's too-big cock ripped his boy-hole a little. He whimpered a little, but when Tadashi tried to take it out in panic, Hiro practically screamed, "N-NO!" Tadashi looked at Hiro with angst and concern. Hiro looked at him with a pleading face. "P-please don't… I've been fanaticizing this for 3 years… D-don't stop now…" Tadashi nodded and slowly pushed himself back in all the way. He began to thrust slowly, doggystyle, riding his little brother's ass with his entire crotch. He moaned as he felt Hiro's walls tighten up every time he went deeper.

Tadashi gasped as he felt something warm lap at his knees; he looked down to see that Hiro had peed himself. Hiro looked embarrassed, but neither of them could stop now. He continued thrusting until he couldn't take it anymore, spilling his hot seed deep inside Hiro's ass, streaking it along his walls and spilling out onto his butt and Tadashi's crotch. He pulled out and slowly crawled over to the camera and turned it off. He looked at Hiro, who was already beginning to fall asleep. He smiled and, feeling his exhaustion too, he picked Hiro up and carried him to Hiro's bed, which was clean. _"I guess we'll just have to clean up tomorrow…"_ He heard the phone ring downstairs, but decided to just leave it, opting instead to crawl in next to Hiro. He quickly fell asleep against his little brother's naked body, hearing Hiro's soft breaths and quiet heartbeat fade into the blackness of sleep…

* * *

><p><em>"This is Cass; I'm not here at the moment, so leave a message and I'll get back to you as soon as I can. Thank you!" <em>*BEEP* "Hello? Boys? The storm is getting pretty bad, so it looks like I'm gonna spend the night in a Marisawa hotel. I'll see you around noon tomorrow. YOU BETTER HAVE A GOOD REASON TO NOT ANSWER! YOU BETTER BE SLEEPING AND NOT IN JAIL! 'K love you guys!" *BEEP*

**Authors Note II: **Oh my… I… Didn't expect that… Either way, I'm tired, but I hope you guys like it! I'll keep this Authors Note short, so I will see you all in my Naruto fic!

**Songs I listened to while typing:**

Magical Mirror (Len and Rin Kagamine)

The Wolf that That Ran Away with Little Red Riding Hood (Len and Rin Kagamine)

The Sea of One Thousand Fathoms, The Shore Sands of Ten Thousand Miles (Len and Rin Kagamine)

Corrupted Flower (Len and Rin Kagamine)

***EXTRA NOTE***

You guys REAAALLY wanted it, so chapter two will be out at 6 in the morning, California time (or earlier!), January 1st, 2015. :D :D :D


	2. Chapter 2

**"Hiro, My Little Test Subject"**

_By MaturePopcorn_

**Description: **When Tadashi decides to make Baymax, he needs a LOT of information for him about people and the human body. But Baymax can only learn _so much_ from books and the internet; some of it has to come from real-life experiences. And who better to help Tadashi than his own brother…

**WARNING: **No warning here; the first chapter should have clued you in to what was going on in THIS fic. *mischievous grin* But I will give a fluff warning; this story is mainly to advance the (confusing and WTF) plotline… Sorrs! But yeah, I'll try to (maybe) work something in.

**_Author's note:_** Ermagersh I totally thought this would be a one-shot, but I really wanna write more about them…! And I was reading the reviews today… Hiro is, indeed, a slight masochist. :o Ah well, whatever makes 'em happy! :p So anywayz, here is the beautiful chapter 2 of (?).

Sooo much love,

~Kisa Alvarez

**Chapter 2**

Tadashi woke up slowly and groggily, not wanting to even move. He had practically passed out on the bed from sheer exhaustion after his little "scientific data collecting" incident. He looked down and saw his little brothers face buried into his bare chest, and felt him breathing slowly and quietly. He could feel Hiro's heart beating against his stomach and felt his smooth legs against his own. He smiled, remembering what they had done the previous night. He slowly sat up and stretched and, in the process, untangled himself from Hiro's body. Hiro moaned in protest as his older brother left his side. He moved over, with his eyes still closed, and snuggled his head against Tadashi's hip. Tadashi watched with eyes full of love and ran his hand over the younger boy's messy black hair.

…Then he looked up at the clock and nearly had a heart attack.

"Shit!" he yelled, jolting Hiro awake as he jumped out of bed saying, "Shit, shit, shiiit…!"

Hiro yawned and stretched, looking at Tadashi with bored, exhausted eyes. "What the hell, Tadashi?"

Tadashi looked at Hiro while trying to pull on pants. "It's 10:27!" he yelled, throwing clothes at the younger boy.

Hiro yawned again. "So? It's Sunday. You don't have classes today, and the bakery's closed."

Tadashi looked at Hiro. "Aunt Cass…!"

Hiro's eyes widened as the information clicked. "SHIT! TADASHIII!"

Tadashi looked pissed and worried. "Put some clothes on; we'll just act like nothing happened. Okay?"

Hiro hopped out of bed and threw a shirt on. "Yeah, I know."

When both boys were fully clothed, they ran downstairs to find an empty bakery. The lights were all off, and the voicemail machine was blinking red. Tadashi walked over to the machine with forced calmness and listened to the single message. He sighed heavily, "Oh thank fucking god…" He looked at Hiro, completely exhausted. "Aunt Cass spent the night in Marisawa hotel; she'll be back at noon."

Hiro sighed. "We got up for nothing?" He crossed his arms and headed back to their room. "Screw this, I'm going back to sleep."

Tadashi grabbed his navy blue hoodie. "Wait. Maybe it's not a waste." He pulled out a pen and notepad from the drawer behind the counter and scribbled a note, saying the words as he went. "Aunt Cass: We are going out for a bit to see a movie, etc. We'll be back by 8:00 tonight. Love, Tadashi and Hiro." He looked at Hiro and smiled. "'K?"

Hiro sighed. "I'm tired. You better buy me caffeine…"

Tadashi smiled and pulled the door open, letting Hiro out first. He locked up behind him and followed the younger boy, glancing at his ass when no one was looking as they walked down the street to the corner store. They walked in and Hiro immediately locked onto the Redbull, making Tadashi frown at Hiro with slight disapproval. "A SMALL one, Hiro."

Hiro glared softly. "It won't kill me…" he mumbled, grabbing the biggest one they carried, a 20 oz. can. Tadashi's left eye twitched, and he sighed. "You have to share."

They walked up and paid, along with a pack of mint gum and a bag of M&M's. As they were leaving, Hiro opened the can and took a huge mouthful, swallowed, and tried to do it again before Tadashi took the can away from him. Hiro whined in protest. "Tadashiii…! Come ooonnn…!"

Tadashi smiled. "Nope. Mine now, lil' bro. Here, have these," he said, handing Hiro the M&M's.

Hiro growled under his breath and muttered, "Overprotective, much?"

Tadashi glanced at Hiro. "Oh, please. After what I did to you last night?" he said lovingly and teasingly.

Hiro blushed. "S-shut up!"

Tadashi just smiled and tussled Hiro's hair, bringing him closer to his body. He didn't even care they were out in public; he just wanted to feel the younger boy's head on his chest as they walked down the twisting streets of San Fransokyo. Besides, it's not like anyone would even notice or care; he was simply holding his little brother out of love. Hiro sighed in muted happiness.

As they walked further along, they stopped at an Italian restaurant. By now it was 11:15, so Tadashi decided it was time for an early lunch. As they walked in, the smell of pasta and bread practically overwhelmed Hiro, who was already starving just looking at the food the servers were bringing out. Tadashi looked at Hiro and smiled. "Hungry?" Hiro nodded vigorously. A server, about 16 with fair hair and green eyes, appeared out of the kitchen. "Hello! Welcome to Venticellos. I'll seat you over here by this window," the boy said, leading them to a seat over by the far end of the building, near the back door. They sat down and another waiter brought out two glasses of water and a basket of breadsticks. Hiro immediately grabbed two and took a huge bite of one. Tadashi chuckled. "Hiro, slow down. I'll leave some for you," he said, grabbing one.

"I dnt ker, mm hngry," Hiro mumbled, mostly to himself.

Tadashi smiled. "Well, I have to pee, so just wait here and eat ALL the breadsticks, then." He smiled and got up, walking over to where the hallway led to the bathrooms. He opened the door to the single roomed unisex bathroom and before he could lock the door, Hiro pushed his way in, smiling at Tadashi. Tadashi sighed. "What, I can't even pee in silence?"

Hiro grinned wider. "Nope!" He hopped up onto the sink and pulled out his phone, opening Clash of Clans. Tadashi just sighed and turned to the toilet, which was under a window looking out onto a heavily treed back area, and went. When he was done, he turned around…

…And Hiro's pants were on the floor. His eyes widened. "Uhm… 'K, Hiro? What are you DOING?"

Hiro smiled naughtily. "Come on, bro, I'm bored."

Tadashi sighed again. "Hiro, I'm still exhausted from last night. Are you sure you can't wait?"

Hiro whined. "Come ooon, Tadashi…! At least blow me then…!" He got up off the sink and grabbed Tadashi's hands, drawing them to his hard boyhood. He shoved one of Tadashi's hands down his underwear and used his free hand to grab Tadashi's head, forcing the older boy to bend down so they could kiss. Hiro forced his tongue down Tadashi's throat. They kissed so passionately they forgot where they were or what they were doing; they didn't even care that a server would probably clear their table. They just wanted each other.

When they finally pulled away to breath, Hiro moaned softly. "Come ON, Tadashi. I know you want this too."

Tadashi closed his eyes and rested his head on Hiro's shoulder. "Nmmh… Hiro, I love you so much."

Hiro smiled. "I love you too, big bro."

Tadashi opened his eyes. "I'm still not gonna fuck you."

Hiro growled in annoyment. "Damnit Tadashi!"

Tadashi pulled his head away and blinked, realizing where they were again. "I better go make sure our table isn't cleared. Come on," he said, grabbing Hiro's hand gently.

Hiro pulled away. "I gotta pee."

Tadashi twitched. "NOW you have to pee. 'K, well, just meet me at the table when you're done." He opened the door and walked back to their table, which hadn't had been cleared yet, and sat down. He took a bite of a breadstick and, when a waiter came by, ordered ravioli for himself and linguini for Hiro, noting the younger boy's odd obsession with it.

Five minutes passed, then ten. Tadashi sighed expectantly and walked over to the bathroom. He knocked on the door and got no response. He tried to open it, but it was locked. "Hiro?" he called. No response. A waitress came by and walked over to Tadashi.

"Is everything ok, sir?"

Tadashi looked at her nervously. "Umm… My brother's been in there for 10 minutes and he isn't answering me…"

The waitress blinked. She pulled a key from her pocket. "Here, this is for the bathrooms."

Tadashi thanked her and unlocked the door, opened it, and had a half heart attack, half panic attack. The window was wide open, and there was no boy in the room. Tadashi started to think Hiro was playing a trick, a stupid trick that would ultimately end with going straight home… Until he saw Hiro's phone, still on the counter, along with his wallet and the necklace that Tadashi had given him three years ago. Something was CLEARLY not right.

"H-Hiro?" Tadashi walked over to the window. "Hiroooo!" He called out into the wooded area, but no reply came. He looked around, but there was nothing. Nothing at all…

**Authors Note II: …Ummm… *Flinches* Please don't attaaack me…! YES I AM WELL AWARE THIS IS *checks calendar* Ummm 25 DAYS LATE! Weahhh…! Gomen, guys! I've been so busy with school and etc. that I haven't had time! *whimpers* But… here it is, I guess! I also apologize for it not being what anybody expected, including me… I have NO idea why I wrote what I did just now… exhaustion? IDK. Off topic, has anyone else seen Neon Genesis Evangelion? Probably, it's so old… It's funny, though! I knew it existed, but finally got around to watching it in 2015, the year it takes place. And the second impact was the year I was born! Huh… :o Anyway, I'll see you all in the extremely off topic third chapter (No, I'm not setting a due date, sorry! Look how well it worked last time…) Again, sorry for the lateness and fluff! Oi… :/**

**Songs I listened to while typing:**

Magical Mirror (Len and Rin Kagamine)

The Wolf that That Ran Away with Little Red Riding Hood (Len and Rin Kagamine)

【作業用BGM】ボカロVOCALOID曲メドレー70曲


End file.
